1. Field of the Invention
The present invention relates to an antenna device used in various types of wireless communication apparatuses, such as mobile telephones provided with a folding structure. The present invention also relates to an antenna device whose antenna operation is switchable by opening and closing a casing and to a wireless communication apparatus.
2. Description of the Related Art
Various types of antennas, such as whip antennas, are used in mobile telephones. Antennas that protrude from the casing, such as whip antennas, are functionally excellent, but they are inconvenient in that they protrude from the casing, and this interferes with storage and retrieval. For this reason, antennas that are built into the casing have come to be used.
In relation to such antennas built into the casing of mobile telephones, there is a mobile telephone where plural antennas are built into a foldable casing, with stable antenna characteristics and communication quality being excellently maintained without relation to the opening and closing of the casing (e.g., see Japanese Patent Application Laid-Open Publication (JP-A) No. 2002-368850, paragraph no. 50 and FIG. 12). There is also a mobile telephone configured to switch plural antennas (e.g., see JP-A No. 2002-368850, paragraph no. 53 and FIG. 15). There is also a mobile telephone where two antennas are built into a foldable casing, with one antenna being usable in a state where the casing is folded and the other antenna being usable in a state where the casing is not folded (e.g., see JP-A No. 2003-204281).
In wireless communication apparatuses such as mobile telephones, the casing is becoming increasingly compact and designed so as to be foldable, and in this type of casing, the disposal space for the built-in antenna is narrow. When an antenna is disposed in a narrow space, the antenna element comes into close proximity to the grounding conductor (GND), and in wireless communication apparatuses provided with a folding structure, there is the potential for the distance from the grounding conductor resulting from the opening and closing of the device to cause the antenna characteristics to deteriorate. JP-A Nos. 2002-368850 and 2003-204281 neither disclose nor suggest anything in regard to this problem, and the configurations disclosed in JP-A Nos. 2002-368850 and 2003-204281 cannot solve this problem.